Wax scraper for floating roof tanks

ABSTRACT

A wax scraper for removing waxy deposits from the inside surface of the wall of storage tanks, comprising a floating roof structure floating on product stored in the tank and having affixed thereto a plurality of support means, each support means carrying a scraper blade having scraper blade guiding or controlling means attached thereto for guiding the scraper blades over obstructions, such as seam welds or the like, on the inside surface of the tank as the floating roof structure rises and falls with the level of product stored in the tank.

United States Patent [72] Inventors H rold A- Mle 3,422,981 1/1969 McBrien et al. 220/26 S co l po 2,846,] l 8/1958 Stoyer 220/26 Ardell I-l. Nelson, Coraopolls; Franklin R. 2,897,998 8/1959 U|m.... 220/26 Neely, Sewlcldey, all 0! P8. 2,960,252 I l/l960 Ulm 220/26 3w;- 3 3 1969 FOREIGN PATENTS i e une Patented Nov. 9,19." 539,813 4/l922 France 48/176 [73] Assignee Pittsburgh-Des Molues Steel Company Primary Examiner-Stephen J. Novosad Pittsburgh, Pa. Assistant Examiner-Lawrence J Staab Attorney-Shoemakera Mattare [54] WAX SCRAPER FOR FLOATING ROOF TANKS 23 Claims, 12 Drawing Figs.

[52] U.S. Cl 220/26 S,

' 15/2465 48/176 ABSTRACT: A wax scraper for removing waxy deposits from [51] lnLCl 865d 87/20 h i id surface f th wall of storage tanks, comprising a I] Field of Search. 15/] .7, fl i f Structure floating on product stored in the tank 24 -5, 3; 16 /1 48/176, and having affixed thereto a plurality of support means, each 178; 23/2599 support means carrying a scraper blade having scraper blade guiding or controlling means attached thereto for guiding the [56] References Cned scraper blades over obstructions, such as seam welds or the UNITED STATES PATENTS like, on the inside surface of the tank as the floating roof struc- 3,398,85l 8/1968 Challenger et al 220/26 S ture rises and falls with the level of product stored in the tank.

7 "R ','T" 3 L fl? -s J fill PATENTEDHUV 9 l9?! 3,618,812

SHEET 1 BF 3 INVENTORS HAROLD A. MAEDER ARDELL H. NELSON 8| FRANKLYN R. NEELY ATTORNEYS PATENTEDuuv 9 l97l 3,618,812

sum 2 UF 3 INVENTORS AM- HAROLD A. MAEDER ARDELL H. NELSON 8| FRANKLYN R. NEELY ATTORNEYS PATENTEDNU? 9 :sn

SHEET 3 [IF 3 llo INV ENTORS HAROLD A. MAEDER ARDELL H. NELSON a FRANKLYN R. NEELY ATTORNEYS WAX SCRAPER FOR FLOATING ROOF TANKS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a wax scraper for removing waxy deposits from the inside surface of floating roof storage tanks during the operation of such tanks without requiring the removal of all obstructions from the inside surface of said tanks.

2. Prior Art In the oil industry, crude oil and like products are stored in large storage tanks for later refining and other processes to be performed on the stored product.

Such a storage tank comprises a cylindrical shell with or without a permanent roof and having a roof within the tank arranged to float on the product stored therein. Due to the large size of the tanks, some space must be provided between the rim of the floating roof and the tank shell to prevent canting and binding of the roof in the shell. This annular space must be sealed to prevent product loss by evaporation and unreasonable contamination of the stored product. Well-known flexible tube-seal assemblies are generally provided in this space for this purpose.

Some products stored in the tanks deposit waxy substances on the tank shell during successive empty and full cycles. This accumulated waxy deposit melts during hot weather and runs down the shell and often flows onto the roof deck thereby creating a hazardous situation as well as a maintenance problem. Proper functioning of the seal assemblies is also impeded by the waxy deposit.

Recently, there has been a sharp increase in interest and processing of low sulfur crudes, which have a high wax content but result ultimately in a lesser amount of air pollution during burning of the refined oil. Higher sulfur crudes have a lower wax content and therefore do not present as serious a problemwith respect to waxy deposits but they require additional processing operations to achieve the same reduction in air pollution as the low sulfur crudes. Thus, the oil industry has a need for a device to remove and to prevent the waxy deposits from building up during operation of the floating roof. of air pollution during burning of the refined oil. Higher sulfur crudes have a lower wax content and therefore do not present as serious a problem with respect to waxy deposits but they require additional processing operations to achieve the same reduction in air pollution as the low sulfur crudes. Thus, the oil industry has a need for a device to remove and to prevent the waxy deposits from building up during operation of the floating roof.

Various forms of wax scrapers are now in use but, for effective removal of the waxy deposit from the interior of the tank, they require that all projections, burrs, weld deposits, etc. be removed from the inside of the tank shell to enable free movement of the wax scraper and floating roof structure without becoming caught on such projections or the like. In addition, the wax scrapers now generally in use interfere with proper functioning of the seal, or are exposed to air thus creating a spark hazard and are also prone to wear out quickly.

SUMMARY OF THE INVENTION The present invention solves all of these problems by providing guide members and by arranging the scraper assembly in a particular manner to guide the scraper blade over obstructions on the inside of the tank shell thus eliminating the need for grinding obstructions flush with the inside surface of the tank shell. Further, the scraper assembly is spaced from the floating roof seal thus not interfering with proper functioning of the seal; the scraper blade is self-sharpening; and the scraper assembly is entirely submerged in the stored product thus ensuring nonsparking operation and self-lubrication of the scraper.

Accordingly, it is an object of the invention to provide a wax scraper carried by a floating roof assembly and which scraper can be used with a variable rim space of from 3 inches minimum to 12 inches maximum, for example.

Another object is to provide a wax scraper which is entirely submerged in the stored product thus having nonsparking operation.

A further object is to provide a wax scraper which is practically maintenance-free and which has a long life.

A still further object is to provide a wax scraper which is self-sharpening and self-lubricated.

Yet another object is to provide a wax scraper which is nonclogging and which does not interfere with proper functioning of the seal.

An even further object is to provide a wax scraper which is simple to make and use and which is reliable in operation.

A further object is to provide a wax scraper which is flexible thus being capable of conforming to irregularities or variations in tank shell geometry.

A specific object is to provide a wax scraper which is guided over obstructions on the inside of the tank shell thus eliminating the need for grinding these obstructions flush with the shell surface which, in some instances, weakens the walls of the tank.

Other objects and advantages will become apparent from a study of the following detailed description and drawings of the preferred embodiments of my invention wherein like reference numerals refer to like parts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view in elevation of a floating roof assembly with a scraper carried thereby according to the present invention.

FIG. 2 is a cross-sectional plan view of the tank with floating roof and scraper taken along line 2-2 in FIG. 1.

FIG. 3 is a perspective view of a pair of adjacent scraper assemblies such as shown in FIG. 1.

FIG. 4 is an enlarged partial cross-sectional view in elevation of one of the scraper assemblies shown in FIG. 1.

FIG. 5 is a cross-sectional view in elevation of a pair of scraper assemblies taken along line 5-5 of FIG. 4 showing the vertical offset and end overlap of adjacent scraper blades.

FIG. 6 is a cross-sectional view in elevation of a modification of the invention shown in FIGS. 1 and 3.

FIGS. 7a-7c illustrate diagrammatically the action of a scraper assembly as it approaches, rests on, and passes an obstruction while the roof is moving downwardly, and

FIGS. 8a-8c illustrate diagrammatically the action of a scraper assembly as it approaches, rests on, and passes over an obstruction while the roof is moving upwardly.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a tank T having a cylindrical shell S, bottom B, and roof R, which may or may not be provided, is shown. Disposed within shell S is a floating roof FR floating on stored product P and comprising a bottom 1 having a peripherally upstanding rim 2 carrying around its upper peripheral edge a weather seal 3 for preventing rain, etc. from entering between floating roof FR and shell S when a permanent roof R is not provided. Also carried by the peripherally upstanding rim 2 is a tube seal assembly 4 disposed in sealing and sliding relationship between upstanding rim 2 and shell S. Tube seal assembly 4 and weather seal 3 prevent undue contamination and evaporation of stored product P. Fixedly attached as by welding, for example, around the peripheral underside of bottom 1 are a plurality of downwardly extending channel-shaped mounts or legs 5 having a pair of vertically spaced holes 8a and 8b in the lower end thereof. Pivotally attached in alternate ones of said holes and 8b in adjacent legs 5 as by a bolt 7 are a plurality of vertically staggered or offset upwardly and outwardly extending channel-shaped arms or supports 6 pivotally carrying scraper assemblies 9 at the upper end thereof. As can be seen in FIG. 2, legs 5, arms 6, and scraper assemblies 9 are disposed around the entire circumference of shell S.

Referring now to FIG. 3, scraper assemblies 9 are shown in more detail as comprising a pair of bottom guide members 11 pivotally attached to the upper end of channel-shaped arm 6 as by a bolt 12 passed through guides 11 and the flanges of channel-shaped arm 6. Guides 11 are fixed along one edge 1 lb near the center of one side of an elongate flexible metal scraper blade 13, and a top guide 14 is fixed to the center of the other side of scraper blade 13 and extends transversely therefrom. Scraper blade 13 has a cutting edge C struck at an angle of approximately 45 relative to the blade; and guides 11 and 14 have wall-engaging protruding portions 11a and 14a, respectively.

As shown in FIG. 4, scraper assembly 9 is biased into sliding contact with shell S with a force P, by a hair-spring l looped around bolt 7 and having one end 10a disposed against web 6a of channel-shaped arm 6 and the other end 10b disposed against web a of channel shaped leg 5.

As shown in FIG. 4, when floating roof structure FR is moving downwardly within shell S in the direction of arrow A, the force P is being applied to scraper assembly 9 which force can be resolved into its horizontal and vertical components P, and P, respectively. In addition, the force P, is being exerted on the scraper assembly 9 by spring 10 and in the position shown, this spring force exceeds the horizontal component of force P such that scraper assembly 9 is maintained in firm contact with shell S.

Still referring to FIG. 4, the scraper assembly 9 is not encountering any obstructions and the rim space S between rim 2 and shell S is approximately 8 inches. The scraper blade 13 defines an acute angle a of approximately 45 with respect to shell S and cutting edge C of blade 13 is disposed at an angle ,8 of approximately 90 with respect to shell S. In this particular arrangement or position of parts, the horizontal and vertical components of the various forces involved and the angle of attack of scraper blade 13 is such as to achieve maximum scraping effect with minimum force required. Scraper assembly 9 is capable f effectively and efficiently scraping waxy deposit D from the inside surface of shell S from a minimum rim space RS of 3 inches to a maximum rim space RS of 12 inches.

In FIG. 5, the overlap b and vertical spacing a of adjacent scraper blade 13 is shown. In practice, for a storage tank T having a diameter of approximately 130 feet the vertical spacing a is approximately linches and the end overlap b is approximately 2 inches.

An embodiment of the invention show in FIGS. 1-5 is shown in FIG. 6. In this embodiment, a leaf spring 15 has merely been substituted for arm 6 and hairspring 10. The leaf spring 15 has one end 15a extending between guides 11 sand looped around bolt 12 and the other end folded closely around bolt 7 with a looped part 15c and having the free end 15b disposed against web 50 of leg 5. All of the details of the scraper assembly 9, floating roof and tank are identical to the FIG. 1-5 embodiment.

FIGS. 7a-7c show the action of the scraper assembly 9 as it is moving down inside shell S. In FIG. 7a, bottom guide 11 has encountered seam weld W and has begun to guide scraper blade 13 outwardly around the weld. Actually, the scraper assembly 9 is pivoting about the point llla on bottom guide 11. In this position, spring force P, exceeds the horizontal component P, of force P, maintaining the scraper assembly 9 in firm contact with shell S.

In FIG. 7b, the cutting edge C of scraper blade 13 has contacted seam weld W a resulting increase in the resistance to downward movement of scraper assembly 9, thereby causing an increase in force P and a corresponding increase in horizontal component P,, P, now exceeds spring force P, and due to the pivoting action of the scraper assembly about point 11a, angle a has increased and angle B has decreased so that scraper blade 13 is now quite readily guided out and over seam weld W without creating undue stress in the scraper assembly. As the scraper blade 13 moves over seam weld W and the resistance to movement of the scraper blade 13 decreases, the spring force P, gradually exceeds the horizontal component P, of force thereby ensuring that scraper blade 13 remains in firm contact with shell S at all times.

In FIG. 7c, scraper blade assembly 9 has traversed seam weld W and is once again disposed in its normal scraping posi tion, namely angle a is approximately 45 and angle B is approximately and the spring force P, exceeds the horizontal component P, of force P. Thus, the scraper assembly 9 of the present invention effectively scrapes away waxy deposit D, regardless of whether an obstruction such as seam weld W is encountered or not, and when such obstructions are encountered undue stresses are not created in scraper assembly 9.

FIG. 8a-8c depict the operation of the scraper assembly 9 as the floating roof structure and scraper assembly 9 are moving upwardly inside shell 5. As can be seen, when scraper assembly 9 is moving upwardly, bottom guide 11 is spaced from shell S and point of top guide 14 is in contact with shell S an scraper blade 13 defines an angle a of approximately 30 with respect to shell S. As it is moving upwardly, scraper assembly 9 has both spring force P and horizontal component P, of force P urging it into finn contact with shell S. Scraper blade 13 also scrapes away waxy deposit D during its upward movement.

In FIG. 8b, the point of scraper blade 13 is resting on seam weld W and scraper assembly 9 is pivoted outwardly around point 14a, which has the effect of decreasing angle 01' thereby lessening the resistance to upward movement of scraper blade 13.

In FIG. 80, the scraper blade 13 has passed over seam weld W and has once again resumed its normal scraping position wherein angle is approximately 30.

While the operation of the invention has been described with reference to the FIG. 1 embodiment, it should be noted that the operation of the FIG. 6 embodiment is identical to the operation of the FIG. 1 embodiment.

In both embodiments illustrated, the elongate scraper blade 13 is sufficiently flexible to accommodate itself to variations in the shell geometry. The various components comprising the scraper assembly of the present invention may obviously be made from any suitable material such as, for example, metal; and various forms of pinned or even notched connections may be substituted for the bolts 7 and 12.

The wax scraper blade is efiiciently and effectively moved over obstructions on the inside surface of the tank as the floating roof rises and falls with the level of stored product by means of scraper blade guiding or controlling means projecting therefrom and movable therewith as hereinbefore described.

The specific embodiments described are intended as illustrative only and not restrictive, various other modifications and arrangements as are obvious to one having ordinary skill in the art being possible without departing from the scope and spirit of the invention.

We claim:

1. A wax scraper for floating roof storage tanks having a tank shell wherein a roof is arranged to float on product stored in said tank, comprising a bottom for said roof having an annular peripherally upstanding rim carrying seal means to slidably seal said roof with respect to the tank shell, a plurality of downwardly extending support means fixed to the peripheral underside of said bottom in radially inwardly spaced relationship to said tank shell and carrying on their lower ends scraper means yieldable biased into sliding contact with said tank shell to scrape waxy deposits from said tank shell as said floating roof rises and falls with the level of stored product, and guide means connected to said scraper means and in operative-sliding engagement with said tank shell for effecting movement of said scraper means inwardly of the shell when said scraper means passes over an obstruction on the inside surface of the shell and thus allow the scraper means to move vertically upwardly or downwardly uninterruptedly in the shell 2. A wax scraper as defined in claim 1 wherein said plurality of downwardly extending support means and scraper means are annularly arranged to scrape substantially the entire inner surface of said tank shell.

3. A wax scraper as defined in claim 2 wherein adjacent scraper means are vertically offset with respect to one another.

4. A wax scraper as defined in claim 3 wherein alternate scraper means are arranged in a first plane and the scraper means interposed between said alternate scraper means are arranged in a second plane vertically spaced from said first plane.

5. A wax scraper as defined in claim 2 wherein adjacent scraper means overlap at their ends.

6. A wax scraper as defined in claim 3 wherein each of said support means has adjustment means thereon to selectively vertically adjust said scraper means in said vertically offset relationship.

7. A wax scraper as defined in claim 2 wherein said downwardly extending support means comprises a plurality of elongated channel-shaped legs and each of said scraper means includes an elongated arm pivotally attached at one end to the lower end of its associated leg and defining an acute angle with said leg, the other end of said arm having a scraper blade assembly pivotally attached thereto.

8. A wax scraper as defined in claim 7 wherein spring means is arranged between said arm and said leg yieldably urging them angularly apart.

9. A wax scraper as defined in claim 7 wherein guide means including bottom guide means are carried by said scraper blade assembly, said bottom guide means being pivotally attached in generally parallel relationship to said other end of said arm, and an elongated scraper blade attached generally in the center thereof to one edge of said bottom guide means and extending transversely thereto.

10. A wax scraper as defined in claim 9wherein a top guide means is fixed to the opposite side of said scraper blade intermediate said bottom guide means.

11. A wax scraper as defined in claim 10 wherein said bottom guide means comprises a pair of flat elongated parallel guide members pivotally attached to said arm on opposite sides thereof and being fixed to said blade at spaced locations, said top guide means comprising a flat elongated guide member parallel to said bottom guide means and fixed centrally of said blade opposite said bottom guide means.

'12. A wax scraper as defined in claim 6 wherein said support means comprises a plurality of downwardly extending channel-shaped legs and each of said scraper means includes an elongated arm, said adjustment means comprising a plurality of vertically arranged holes in each of said legs with one end of each of said elongated arms pivotally attached in one of said holes, each succeeding am being attached in an alternating fashion in a hole vertically spaced from the hole in which the preceding arm is attached. 7

13. A wax scraper as defined in claim 5 wherein said downwardly extending support means comprises a plurality of elongated channel-shaped legs and each of said scraper means includes an elongated arm pivotally attached at one end to the lower end of its associated leg and defining an acute angle with said leg, the other end of said arm having a scraper blade assembly pivotally attached thereto, said scraper blade assembly comprising a pair of parallel spaced flat-elongated bottom guide members pivotally connected to said other end of said arm on opposite sides thereof and generally parallel thereto, an elongated scraper blade fixed to one edge of said bottom guide members in transverse relationship to said guides, and a single flat elongated top guide member fixed centrally of said scraper blade opposite from said bottom guide members and extending transversely therefrom.

14. A wax scraper as defined in claim 13 wherein said elongated arms are selectively vertically adjustably mounted on said elongated legs.

15. A wax scraper as defined in claim 14 wherein said adjustable mounting comprises a plurality of vertically arranged holes in each of said legs, alternate arms being pivotally attached in a first of said holes with the intermediate arms being pivotally attached in a second of said holes whereby adjacent arms are vertically ofiset from one another.

16. A wax scraper as defined in claim 15 wherein said bottom and top guide members each have widened portions defining a protrusion thereon, said protrusion on said bottom guide being in contact with said shell and said protrusion on said top guide being spaced from said shell during downward movement of said roof and scraper blade assembly; said protrusion on said top guide being in contact with said shell and said protrusion on said bottom guide being spaced from said shell during upward movement of said roof and scraper blade assembly; said scraper blade normally defining an angle of approximately with said shell and having a cutting edge disposed at an angle of approximately 90 relative to said shell during downward movement of said roof and scraper blade as sembly; and said scraper blade normally being inclined at an angle of approximately 30 relative to said shell during upward movement of said roof and scraper blade assembly; whereby during downward movement of said roof and scraper blade assembly said protrusion on said bottom guide acts as a pivot point about which said scraper blade assembly pivots when an obstruction such as a seam weld is encountered by said scraper blade assembly to thereby change the angular disposition of said scraper blade and cutting edge relative to said shell so that said scraper blade is pulled over and around said obstruction with relative ease and without creating undue stress in said scraper blade assembly during said downward movement; and said protrusion on said top guide acts as a pivot point for said scraper blade assembly during upward movement of said roof and scraper blade assembly when said scraper blade assembly encounters an obstruction such as a seam weld such that the angular disposition of said scraper blade is changed relative to said shell so that said scraper blade assembly is moved over obstructions with relative ease and without creating undue stress in said scraper blade assembly during said upward movement.

17. A wax scraper as defined in claim 16 wherein spring means is disposed between said arm and said leg biasing the scraper blade into firm sliding contact with said shell, and said scraper blade if flexible.

18. A wax scraper as defined in claim 17 wherein said arm comprises a leaf spring having one end pivotally attached to said leg and the other end pivotally attached to said bottom guide members, said leaf spring biasing said wax scraper into contact with said shell during upward and downward movement of said roof and scraper blade assembly.

19. A wax scraper for tanks having waxy deposits adhered to the inner surface of the wall thereof, comprising: a floating roof structure in sealed sliding relationship with the wall of the tank and floating on product stored in said tank; scraper blade means carried by said floating roof structure; means urging said scraper blade means into sliding contact with the wall of the tank; and guide means, connected with said scraper blade means, for guiding and effecting movement of said scraper blade means inwardly of the shell when said scraper blade means passes over an obstruction on the inside surface of the shell to thus allow said scraper blade means to move vertically upwardly or downwardly uninterruptedly over any obstructions, such as seam welds or the like, as the floating roof structure rises and falls with the level of product stored in said tank.

20. A wax scraper as in claim 19 wherein said scraper blade means includes a plurality of spaced apart stationary support means carried by the floating roof structure and spaced inwardly from the wall of said tank.

21. A wax scraper as in claim 20 wherein movable means are secured to each of said support means.

22. A wax scraper as in claim 21 wherein each of said movable means has a scraper blade attached thereto.

23. A wax scraper as in claim 22 wherein said scraper blades are elongated and are generally horizontally disposed and said guide means project generally vertically from opposite sides of each of said scraper blades and move therewith as the floating roof structure rises and falls. 

1. A wax scraper for floating roof storage tanks having a tank shell wherein a roof is arranged to float on product stored in said tank, comprising a bottom for said roof having an annular peripherally upstanding rim carrying seal means to slidably seal said roof with respect to the tank shell, a plurality of downwardly extending support means fixed to the peripheral underside of said bottom in radially inwardly spaced relationship to said tank shell and carrying on their lower ends scraper means yieldable biased into sliding contact with said tank shell to scrape waxy deposits from said tank shell as said floating roof rises and falls with the level of stored product, and guide means connected to said scraper means and in operative-sliding engagement with said tank shell for effecting movement of said scraper means inwardly of the shell when said scraper means passes over an obstruction on the inside surface of the shell and thus allow the scraper means to move vertically upwardly or downwardly uninterruptedly in the shell
 2. A wax scraper as defined in claim 1 wherein said plurality of downwardly extending support means and scraper means are annularly arranged to scrape substantially the entire inner surface of said tank shell.
 3. A wax scraper as defined in claim 2 wherein adjacent scraper means are vertically offset with respect to one another.
 4. A wax scraper as defined in claim 3 wherein alternate scraper means are arranged in a first plane and the scraper means interposed between said alternate scraper means are arranged in a second plane vertically spaced from said first plane.
 5. A wax scraper as defined in claim 2 wherein adjacent scraper means overlap at their ends.
 6. A wax scraper as defined in claim 3 wherein each of said support means has adjustment means thereon to selectively vertically adjust said scraper means in said vertically offset relationship.
 7. A wax scraper as defined in claim 2 wherein said downwardly extending support means comprises a plurality of elongated channel-shaped legs and each of said scraper means includes an elongated arm pivotally attached at one end to the lower end of its associated leg and defining an acute angle with said leg, the other end of said arm having a scraper blade assembly pivotally attached thereto.
 8. A wax scraper as defined in claim 7 wherein spring means is arranged between said arm and said leg yieldably urging them angularly apart.
 9. A wax scraper as defined in claim 7 wherein guide means including bottom guide means are carried by said scraper blade assembly, said bottom guide means being pivotally attached in generally parallel relationship to said other end of said arm, and an elongated scraper blade attached generally in the center thereof to one edge of said bottom guide means and extending transversely thereto.
 10. A wax scraper as defined in claim 9 wherein a top guide means is fixed to the opposite side of said scraper blade intermediate said bottom guide means.
 11. A wax scraper as defined in claim 10 wherein said bottom guide means comprises a pair of flat elongated parallel guide members pivotally attached to said arm on opposite sides thEreof and being fixed to said blade at spaced locations, said top guide means comprising a flat elongated guide member parallel to said bottom guide means and fixed centrally of said blade opposite said bottom guide means.
 12. A wax scraper as defined in claim 6 wherein said support means comprises a plurality of downwardly extending channel-shaped legs and each of said scraper means includes an elongated arm, said adjustment means comprising a plurality of vertically arranged holes in each of said legs with one end of each of said elongated arms pivotally attached in one of said holes, each succeeding arm being attached in an alternating fashion in a hole vertically spaced from the hole in which the preceding arm is attached.
 13. A wax scraper as defined in claim 5 wherein said downwardly extending support means comprises a plurality of elongated channel-shaped legs and each of said scraper means includes an elongated arm pivotally attached at one end to the lower end of its associated leg and defining an acute angle with said leg, the other end of said arm having a scraper blade assembly pivotally attached thereto, said scraper blade assembly comprising a pair of parallel-spaced flat-elongated bottom guide members pivotally connected to said other end of said arm on opposite sides thereof and generally parallel thereto, an elongated scraper blade fixed to one edge of said bottom guide members in transverse relationship to said guides, and a single flat elongated top guide member fixed centrally of said scraper blade opposite from said bottom guide members and extending transversely therefrom.
 14. A wax scraper as defined in claim 13 wherein said elongated arms are selectively vertically adjustably mounted on said elongated legs.
 15. A wax scraper as defined in claim 14 wherein said adjustable mounting comprises a plurality of vertically arranged holes in each of said legs, alternate arms being pivotally attached in a first of said holes with the intermediate arms being pivotally attached in a second of said holes whereby adjacent arms are vertically offset from one another.
 16. A wax scraper as defined in claim 15 wherein said bottom and top guide members each have widened portions defining a protrusion thereon, said protrusion on said bottom guide being in contact with said shell and said protrusion on said top guide being spaced from said shell during downward movement of said roof and scraper blade assembly; said protrusion on said top guide being in contact with said shell and said protrusion on said bottom guide being spaced from said shell during upward movement of said roof and scraper blade assembly; said scraper blade normally defining an angle of approximately 45* with said shell and having a cutting edge disposed at an angle of approximately 90* relative to said shell during downward movement of said roof and scraper blade assembly; and said scraper blade normally being inclined at an angle of approximately 30* relative to said shell during upward movement of said roof and scraper blade assembly; whereby during downward movement of said roof and scraper blade assembly said protrusion on said bottom guide acts as a pivot point about which said scraper blade assembly pivots when an obstruction such as a seam weld is encountered by said scraper blade assembly to thereby change the angular disposition of said scraper blade and cutting edge relative to said shell so that said scraper blade is pulled over and around said obstruction with relative ease and without creating undue stress in said scraper blade assembly during said downward movement; and said protrusion on said top guide acts as a pivot point for said scraper blade assembly during upward movement of said roof and scraper blade assembly when said scraper blade assembly encounters an obstruction such as a seam weld such that the angular disposition of said scraper blade is changed relative to said shell so that said scraper blade assembly is moved over obstructIons with relative ease and without creating undue stress in said scraper blade assembly during said upward movement.
 17. A wax scraper as defined in claim 16 wherein spring means is disposed between said arm and said leg biasing the scraper blade into firm sliding contact with said shell, and said scraper blade if flexible.
 18. A wax scraper as defined in claim 17 wherein said arm comprises a leaf spring having one end pivotally attached to said leg and the other end pivotally attached to said bottom guide members, said leaf spring biasing said wax scraper into contact with said shell during upward and downward movement of said roof and scraper blade assembly.
 19. A wax scraper for tanks having waxy deposits adhered to the inner surface of the wall thereof, comprising: a floating roof structure in sealed sliding relationship with the wall of the tank and floating on product stored in said tank; scraper blade means carried by said floating roof structure; means urging said scraper blade means into sliding contact with the wall of the tank; and guide means, connected with said scraper blade means, for guiding and effecting movement of said scraper blade means inwardly of the shell when said scraper blade means passes over an obstruction on the inside surface of the shell to thus allow said scraper blade means to move vertically upwardly or downwardly uninterruptedly over any obstructions, such as seam welds or the like, as the floating roof structure rises and falls with the level of product stored in said tank.
 20. A wax scraper as in claim 19 wherein said scraper blade means includes a plurality of spaced apart stationary support means carried by the floating roof structure and spaced inwardly from the wall of said tank.
 21. A wax scraper as in claim 20 wherein movable means are secured to each of said support means.
 22. A wax scraper as in claim 21 wherein each of said movable means has a scraper blade attached thereto.
 23. A wax scraper as in claim 22 wherein said scraper blades are elongated and are generally horizontally disposed and said guide means project generally vertically from opposite sides of each of said scraper blades and move therewith as the floating roof structure rises and falls. 